Apparatus for generating or receiving mechanical oscillations



Oct. 15, 1935. I w HAHNEMANN 2,017,695.

G o ECEIVING MECHANICAL osc LATIONS Filed Oct. 21, 1929 2 Sheets-Sheet l kWh/0r: Wa/ferfla/memann :Wfarney zney 2 Sheets-Sheet 2 jkzVenforx Wa/fefflafi/iemmm 65/ w 15% w. HAHNEMANN APPARATUS FOR GENERATING 0R mzcmvme MECHANICAL 6SCILLATIONS Filed Oct. 21, 1929 Oct. 15, 1935.

Patented oer. 15, 1935.

APPARATUS FOR-GENERATING 0B, RECEIV- ING MECHANICAL OSCILLATIONS Walter Hahnemann, Berlin Marienfelde, Germany Application I1()ctober 21, 1929, Serial No. 401,160

Germany May 8 Claims. (Cl. 181 -05) I have filled applications in Germany May 25, 1928; Great Britain July 20, 1929; France July 12, 1929; Italy July 23, 1929.

The present invention relates to sound transmitters and sound receivers, and particularly to transmitters and receivers for submarine signalling. The employment of these devices in other spheres of technical acoustics or in other fields of mechanical oscillations, however, is quite within the scope of the invention. The following description has been confined to the use of the invention for submarine communication for simplicity and ease of explanation.

The apparatus as used in this invention, when of appropriate size and shape, can be used both as a sound transmitter or generator of mechanical oscillations and as a sound receiver or detector of'mechanical oscillations. The following description sets forth several constructions which embozw the principles of the invention.

In sound apparatus, the particular frequency of the oscillations or the band of frequencies with which it is to work is of fundamental importance. In carrying out the invention, a band frequency is selected which approximately lies at the upper limit, of the audible range of frequencies, that is, at 10,000 oscillations or vibrationsper second, or somewhere within the band of frequencies denoted by 5,000 to 20,000 oscillations per second. But the invention is, of course, not

limited to this particular frequency range.

In the frequency band mentioned there are characteristic advantages of considerable practical importance.

Oscillating electric currents having these fre quencies may be used for the generation of sound waves. These electric currents may be generated by mechanical means, that is, by rotating machines, or instead, by oscillating vacuum tube circuits or oscillation generators, unless these devices are excluded for other reasons. when these oscillations are impressed upon appropriate means, well known in the art, e. g. a condenser, the variations of electrical potential will cause vibrations of a frequency corresponding to the frequency of the impressed electrical variations. This will in turn produce sound wa'vesjof a corresponding frequency..

A further advantage to be derived from the use of frequencies in the upper voice, or super-sonant, range is that these frequencies can be modulated and thereby serve as carrier frequencies for conveying speech through a medium such as a liquid, a gas, or a solid. If, for example, a frequency of 10,000 oscillations is chosen, then these oscillations can be satisfactorily modulated to transmit speech by modulating the mechanical oscillations by other frequencies up to, say, 2,500 oscillations per second. This modulation is readily accomplished if the oscillatory systems of the receiver or transmitter are so constructed with regard to coupling and damping that the resulting resonance curves of the circuits necessarily include the modulating frequency within their crests. I

i This frequency-band has its advantages not only for telephonic communication, but also for telegraphic communication by means of heterodyned reception. These methods of communication may be carried out by slight modifications of the invention. If, for instance, the transmitted sound signal, as radiated, has a frequency of 10,000 oscillations per second, and if there are superimposed on the receiver continuous oscillations having a frequency of 9,000 or 11,000 oscillations per second by energizing the receiver from a suitable source of alternating current (high frequency machine, vacuum tube generator, etc.) Y then a heterodyned or beat frequency of 1,000

Furthermore, with the frequencies in question, the' wavelengths are such that the devices are correct, high in efilciency.

The nature of the invention will be more readiiy. understood by reference to the accompanying drawings, whereon:

Fig. 1 is a cross-section through one construc-. tion embodying the invention;

Fig.2 presents a perspectiveview of a modified type of sound transmitter or receiver;

Fig. 2A is a vertical section through the device shown in Fig. 2; v

Fig. 3 is a cross-section of still another form;

Fig. 4 is a side elevation and Fig. 4A is a top or deck-plan of a submarine vessel equipped with apparatus according to my invention; and

Fig. 5 shows the sound transmitter or receiver connected in a circuit.

cillator 0. The oscillator O isconnected with the casing G by an annular fastening member M, which, forv instance, for under-water sound communication is an annular diaphragm. The oscillator O or the whole apparatus has its outer surfaces exposed to the medium through which the compressional waves or sound signal is to be propagated or received. The medium assumed iswater. Airoranyothergasundernormal atmospheric pressure or above 'or below normal pressure may be in the interior of the apparat 'is between the adjacent surfaces of the parts 0 and G. The casing G and the oscillator O-are cylindrical in shape. and acircularend surface-of G is positioned adjacent to a similar surface of 0.

The oscillator is a solid cylinder having a uniform cross-section. The length a of the cylinder is a function of the length of the compressional waves propagated through it. a is in this case equal to If, for example, the oscillator O is made of steel, the speed of propagation of sound therein will be approximately 5,000 meters per second. Thus, if sound waves haying a frequency of 10,000 vibra tions per second are used, their wavelength in this material will be 50 centimeters; since half this wavelength is 25 centimeters, the length of the cylinder would then be 25 centimeters.

In one form of apparatus embodying the invention, the oscillator O is so supported by the annular diaphragm M or otherwise so constructed and disposed that the amplitude of the oscillations of its inner circular or end surface C, immediately adjacent the casing G, is so related to the amplitude of the oscillations of its outer circular or end surface b on the opposite side of oscillator O that is, the surface exposed to the medium of propagation, that the greatest efliciency of energy transfer is attained. Thus, the transformation between the exciting and radiating amplitude is adjusted to secure the bestresults. 1

This may be explained in detail by the following example.

Consider a sound transmitter which is excited by an oscillating electric field undergoing 10,000 alternations per second, the field being confined to the volume between the outer circular-surface of the cylinder 0 and the inner circular surface of the casing G. The oscillator 0 is, with this mode of excitation, electrically insulated from the casing G. This can be most readily effected by inserting insulating material at the junction of parts M and G, or at the junction of parts M and 0. It is well known, as evidenced by prior publications including U. S. Patents to H. C. Harrison, Nos. 1,663,884, 1,678,116, 1,784,871 and 1,788,519, that in a mechanical structure having a greater mass at one end than at the other the amplitude of vibration at the end of smaller mass is greater than the amplitude of vibration at the end of greater mass. 1,678,116 discloses such a structure (see Fig. 37 and page'8, lines 65-116) for coupling two unequal mechanical impedances. Theoretically and experimentally, it has been found that the greatest efficiency in sound transmission isobtained when the amplitude of the vibrations of the inner circular surface of 0, e. g. that adjacent the inner circular surface of G, is one-third of the amplitude of the vibrations of the outer circular surface of 0, e. g. the circular surface of the cylinder 0 remote from the casing. In order to accomplish this the cylinder is made thicker in cross-sectional areaat M or its vicinity or else its mass is increased, as by adding other material of greater specific gravity than 0. Upon adding sufiicient material the cylinder 0 will oscillate in such manner that the amplitude of the oscillations of its inner circular surface will be onethird the amplitude of the oscillations of the outer surface.

It is possible, for example when a reversal of amplitude ratio is desirable. to obtain the amplitude transformation in question by allowing the casing G to oscillate along with the cylinder 0. In this case, the mass of the casing G should be U. S. Patent No.

correspondingly dimensioned so that the casing G may be an oscillatory structure. Generally it has been found preferable to construct the easing G as a non-oscillating member, that is, with G having a comparatively large mass. If it is desired to have the vibrational amplitude of the inner circular surface of oscillator O greater than that of the outer radiating surface of 0, then relatively more mass must be placed at, or near, the outer surface of the cylinder. It has been found desirable, in some instances, to secure the oscillator O to the diaphragm M, which in turn is secured to the casing G, at points near the node line of the oscillations subsequently produced in the oscillator 0.

As is apparent from the above, the sound apparatus is of very simple construction, at least for the frequency band mentioned. With the correct mutual adjustment of the amplitude of the vibrations produced at the inner surface of the oscillator and the amplitude of the vibrations produced at the outer or radiating surface of 0, greater efliciency can be obtained. in transmission. The magnitude of the vibrational amplitude produced at the inner circular surface of the oscillator 0 depends upon-the particular type of excitation used. In this discussion, electrical, e. g. electrostatic, excitation has been assumed although other means are also possible. The magnitude of the vibrational amplitude produced at the outer circular surface of oscillator 0, however, depends upon the medium through which the sound waves are to be propagated. In this discussion, water is assumed to be the medium. The velocity of sound in water is approximately 1,400 meters per second. Thus, the wavelength at sound having a vibrational frequency of 10.000 oscillations per second is about 14 centimeters in water. According to theories well known in acoustics, the damping effect accompanying the use of radiators of zero order (see Physikalische Zeitsohrift 1917, page 261) such as are being considered here, is very considerable if the diameter of the radiating surface is only a fraction of the wavelength of the sound waves being propagated. In practice, the oscillator O is generally designed to have a relatively large crosssectional area, for example, 0 may have a dimeter' of centimeters or more.

In Fig. 2 another form of oscillator is shown, in which the cross-sectional area of the oscillator 0 between the outer and inner circular surfaces is altered for the purpose of obtaining a definite vibrational amplitude transformation. The inner surface has a greater diameter, that is, has relatively greater mass, and therefore a smaller vibrational amplitude, than the outer surface. The transmitter as assembled thus consists substantially of two cylinders of different diameter. The length a of the oscillator 0 not made exactly equal'to half a wavelength of its natural vibrational or resonant frequency, but is made smaller. In the limiting case, with a very great discrepancy in the cross-sectional area of the two circular surfaces of they solid and approximately cylindrical oscillator 0, its length could, for example, be a quarter of a wavelength of its natural vibrational frequency. It always lies between one-quarter and one-half of a wavelength, or between three-quarters and l x and so on.

In Fig. 3, another form of oscillator is shown and is so constructed that the outer surface of the oscillator O has a cross-sectional area of annular shape, while the inner surface has a circular cross-sectional area. This figure discloses an additional construction for producing a desired transformation in the vibrational amplitude of the two surfaces. The radiating surface of this form of the oscillatingmember O is then substantially the area of the annular surface at the outer end of the oscillator 0. The radiating area is therefore smaller than that of the inner surface and this results in an increase in the vibrational amplitude of the oscillations of the outer surface as compared to the vibrational amplitude of the oscillations as produced at the inner surface.

The various forms of oscillator, as shown in Figs. 1, 2 and 3, are given merely as illustrations of constructions for transforming the amplitude of the vibrations travelling between the opposite surfaces of the oscillator 0. There are a great many other forms which the oscillator may assume. These forms will also produce varying amplitude transformations. For instance, the oscillator 0 may be made of two or more materials each having difierent mass or having difierent acoustical properties. In such constructions, the two or more contiguous surfaces of the respective parts of the oscillator should preferably be intimately associated with one another, 'as by welding, soldering or the like. Screws or bolts are not suited to hold this assembly together, because it'is impossible to avoid internal frictional losses at the contiguous surfaces at the high vibrational frequencies used for transmitting and receiving signals with this type of apparatus.

In the following description, a few devices for actuating the sound transmitting or receiving apparatus of this invention are explained in some detail. I

First, means for actuating the sound transmitters or heterodyne receivers will be described.

A changing, oscillating or varying electrical field, magnetic field, or combination of both fields may be used between the oscillator 0 and the casing G, in order to actuate the transmitting or receiving apparatus. An electrical field is pre ferred for practical reasons although other means of excitation may be used besides those enumerated above, and are to be considered as coming within the scope of the invention.

In the apparatus used in connection with this invention, the oscillator O has been disclosed as being an independently oscillating body so constructed as to obtain the desired vibrational amplitude transformation between its radiating surface and its actuated surface. I

The above method of constructing the sound signalling apparatus would lead to apparatus of unmanageably great dimensions when used with low frequency vibrations. But when used with the chosen frequency band the correct type of apparatus isof portable size. invention, as

previously stated, relates to the art of submarine signalling. The propagation of sound waves of such high frequencies as are utilized above actually takes place in water without excessive damping, whereas in air such high frequencies are subject tobe so excessively damped and absorbed that short range communication only is possible. In air much lower frequencies would therefore have to be chosen, and thus modulation of these lower frequencies, by means of superimposed waves having speech frequencies, would then be practically impossible. But heterodyned telegraph signals could still be transmitted by relinquishing the desirable tone produced by mechanical oscillations or compressional waves having 1.000 vibrations per second and choosing a tone fective for transmission is small.

having a considerably lower, or considerably higher, vibrational frequency, as the heterodyning tone. The invention may be used advantageously for transmitting sound in air, however when the above facts are taken into consideration. 5

In the application of the invention to submarine communication, a frequency of 20,000 oscillations per second is not the maximum frequency limit, for sound is efliciently propagated in water even at considerably high frequencies. The very high frequencies necessitate the use of complicated oscillation generators or altemating current generators, such, for example, as vacuumtube generators or high frequency electric machines, which may not be desirable. 10 Moreover, wavelengths would result which for numerous reasons already given would require apparatus for too small for practical construct'ion. If we assum, for instance, frequencies upward of 50,000 vibrations per second, then, for steel in which sound has a speed of about 5,000 meters per second, a wavelength of only 10 centimeters results. Thus the length of the oscillating cylinder 0 will be only 5 centimeters for the case when it is a cylinder of uniform cross-sectional area. In the latter case the inner and outer surfaces would vibrate with the vibrational amplitude of the oscillations of each surface being equal, Since the vibrational amplitude is limited by the character of the vibrating materials, the vibrational amplitude 'utilized must not exceed this limit. As the energy of the transmitted signal is dependent upon the amplitude of the vibrations, it may readily be seen that the energy effective for the transmission of 85 signals is a functon of the sizeof the oscillating body 0, and the body being small the energy ef- At such high frequencies, moreover, the wavelength of the oscillations in water becomes very small, for ex- 0 ample, for oscillations having 50,000 vibrations per second it would be about 3 centimeters. With such short waves any moderately large body submerged in the water would obstruct the sound waves causing a sound shadow andthus would interfere with the exchange of messages between two stations. With oscillations having 10,000 vibrations per second a wavelength of 14 centimeters is obtained. These longer waves are also obstructed by submerged bodies, but less ef- 00 fectively than the waves of higher-frequency.

The invention'is thus concerned with the selection of the most effective frequency band for submarine heterodyne telegraphy or telephony, and the designing of sound signalling apparatus which is as simple in design and as practical in construction as is possible for this selected frequencyv band. The features of the invention are not limited to the frequency band selected or the particular construction of the sound sig- 00 nailing apparatus described in the foregoing p p An additional use of the invention relates to the combination of several of such acoustic devices so that directional effects may be obtained. 05 The arrangements well known in the high frequency art may also be used advantageously in this invention. Since the wavelength of sound .in water, i. e. mechanical oscillations. having 10,000 vibrations per second, is only 14 centi- I as to be practically portable. This again illustrates the desirability of the selected frequency band.

A practical arrangement for this invention is illustrated in Figs. 4, 4A and 5 of the drawings. Figs. 4 and 4A show schematically a submarine with four appliances for transmitting or receiving mechanical oscillations. These four appliances l, 2, 3, 4" operate within the scope of the angles indicated by the broken lines in the drawings. Each of the appliances may be put into operation by the switching arrangement illustrated in Fig. 5.

Fig. 5 is a diagram representing connections for applying electrical energy in order to actuate the oscillator. The casing (21' is grounded. Wire 5 electrically connected to the oscillating body leads to one pole of the direct current generator DC. The wire 6 is connected to the other pole of the drect current generator DC. The excitation of the transmitting apparatus in this case is effected by the establishment of an electrostatic field between plate I1 and the inner surface of O. For this purpose the wire 6 is connected with the electrode H, which is inside the casing G and insulated therefrom. The switch 8 connects the sound transmitting or receiving apparatus to the energizing or detecting apparatus proper for sending or receiving, respectively. In the position shown the circuit is closed for sending, the generator 9 supplying oscillating current to the system under the control of key ID. The choke coils II and I! are inserted to protect the direct current generator DC from the alternating current produced by 9. The direct current is kept from the alternator by condensers l3 and It. When the switch 8 is moved to the position indicated by the dotted line, generator 9 is disconnected and detecting apparatus is connected to what then becomes a receiving circuit. The receiving apparatus may be the usual super-heterodyne receiver IS, the auxiliary frequency being produced by local oscillation generator or a tube oscillation generator I6. After rectification and amplification by H, the signals energize telephone receiver 18 and the signals are thus interpreted.

What I claim isi 1. A device for inter-converting electric and acoustic wave energy and having a casing and a mounting member supported thereby and forming a closure therefor, a vibratory body of substantial mass mounted in said casing solely by means of the mounting member, said vibratory body having its inner end in spaced relation to the casing and its outer end extendingoutside said casing and being of such size and shape and distributed mass that the amplitude of vibration at one end is greater than the amplitude of vibrations at another end.

2. In a device for inter-convertingelectric and acoustic wave energy and'having a casing and a mounting member supported thereby and forming a closure therefor, a vibratory element of substantial mass mounted in said casing, by

size, shape and mass that the amplitude of vibrations at the end proximate the casing is less than the amplitude of vibrations at the end remote therefrom.

3. In combination with a sound transformer device having a casing and a mounting member supported thereby and forming a closure therefor, a vibratory element, an axial length of which is a fractional part of its natural frequency and secured to and supported solely by said mounting member at a point along the axial length of said vibratory element proximate a node line of said element and in spaced relation to said casing. 10

4. In combination with a sound transformer device having a casing and mounting member j supported thereby and forming a closure therefor, a vibratory element of substantial mass and thickness secured to and supported solely by said mounting member in spaced relation to said casing, the mass of said element being so distributed and said element being of such length and being so disposed partially within and partially without said casing that vibrations at one end of the element are substantially greater than vibrations at the other end.

5. In combination with a sound transformer device having a casing and a mounting member supported thereby and forming a closure therefor, a vibratory element of substantial mass and thickness secured to and supported solely by said mounting member at a point proximate a node line of said element and in spaced relation to said casing, said element being disposed partially within and partially without said casing and being of such shape with the mass thereof so distributed that the amplitude of the vibrations at one end is greater than the amplitude of vibrations at another end..

6. In a sound transformer device having a non-oscillatory casing, a flexible mounting member supported thereby and forming -a closure therefor, a vibratory element of substantial mass secured to and supported solely by said mounting member in spaced relation to said casing and disposed partially within and partially without said casing, the mass ofsaid element being such and the mass thereof being so distributed that the amplitude of vibrations at one end of the vibratory element is greater than the amplitude of vibrations at the other end.

7. A device for inter-converting electric and acoustic wave energy and having a casing and a mounting member supported thereby and forming a closure therefor, a vibratory body of substantial mass. extending through said mounting member and supported solely thereby, sai'd vibratory body having its inner end in spaced relation to the casing and its outer end extending through said mounting member outside said casing and being of such size and shape and distributed mass that the amplitude of vibration at one end is greater than the amplitude of vi- 6o bration at the other end thereof.

8. In a device for inter-converting electric and acoustic wave energy and having a casing and a mounting member supported thereby and forming a closure therefor, -a vibratory element of substantial mass extending through said mounting member and supported solely thereby at a node point of said vibratory element, said body having its inner end in spaced relation to said casing, and being of such size, shape and mass that the amplitude of vibration at the end proximate the casing is less than the amplitude of vibration at the end remote therefrom.

WALTER HAHNEIAANN. 

